Not a lot of people. I would be surprised to hear that the game had 1000 logged on at once, including free accounts. That is spread across four servers.
How is the community? What community? There are no guilds, nor is there a reason for them. The forums have about 25,000 registered users, 2500 threads, and 19,000 posts, with “Max users online was 145 @ 08/08/07 11:54 PM.”
There is no real reason to group. You cannot buff or heal, so the only benefits to being around other people are (1) sharing debuffs and (2) dropping things faster due to higher damage. Running solo, I have only had trouble once. I can herd groups of enemies on a mage. Some of the fights might be easier or more interesting in a group, but you can solo the end-dungeon bosses easily enough.
The world channel is better than a free game deserves. /ignore someone every few days and you will have removed pretty much all the problems. Maybe it is worse on the most populated server. The most annoying part is the continuous stream of new players who have not even read the quickstart guide, so they ask questions that are either meaningless or could easily be answered by talking to the NPCs with the big gold exclamation points over their heads. We all enter the world ignorant, pissy, and crying, but you don’t need to enter the internet that way.
There is no community, no reason to form one, and not much means to do so beyond a friends list. How do you get people to recruit their friends or find new ones with the incentive of “you can farm with me”? Oddly, there is a referral program, so you can send your friends a key for a free trial. Think about that one.